There were several causes for the Rajputs' failure. For example, a lot of turmoil inside the states, little contact with central Asian countries so they had very little knowledge of modern warfare techniques. Chivalry was crammed in their very nature along with hatred, trick and treachery. As for the Turks, trickery was an important method of warfare. Thus, while the gallant Rajputs came in the battlefield to die if not win, the Turks moved in after calculating Rajputs' enterprise to live even if they did not succeed.
The Turks had good horses and experienced cavalry which could not be matched by the Rajputs' simple and traditional way of warfare, like their usage of the elephants as the important part in army. They fought desperately, while the Turks fought strategically. So the result was the Rajputs' failure to resists the tactical attacks of the Turks. Rajput pride and the chronic sycophancy of their courtiers were also barriers to learning the new ways to fight the Turks.
After occupying the valley of Ganges and Yamuna (Jamuna), the Turks got many resources that enabled them to keep a large number of soldiers and continue to conquest of other parts of India time after time.
Mahmud of Ghazni (997-1030)
To some historians, the number of Mahmud of Ghazni's invasions in India is 10 and to others it is 17. In North India, there were small Rajputs kingdoms, thus very easy for Mahmud of Ghazni to invade North India and defeat the Rajput rulers. He left some defeated states in the hands of Hindu, Jain and Buddhist kings as the vassel states, except Punjab which served as his headquarters in India. The important places which he conquered were Bhira, Multan, Nagarkot, Thanesar, Qannuj, Mathura, Kalanjar, Gawaliyar and Somnath.
Mahmud's armies stripped the temples in India of their wealth and broke the idols inside them. One of the famous temples is Somnath. There are many stories related to it, one of which tells when Mahmud of Ghazni wanted to break the idol in the temple, the priests requested him not to do so and in return offered him a good amount of wealth. However, Mahmud refused and broke the idols. However, recent researches show that all such stories were fabricated to make him a holy warrior, whereas, the Hindus have many different stories that make him a controversial ruler.